Now for this very special Havel Havelim that Ya'aqov has compiled. There are lots of posts from various Jewish bloggers.

Havel Havelim is a weekly blog carnival on Jewish and Israeli topics. Bloggers send their links in to the week's host, and the hosts can (and should) add other blog posts he/she sees on the net. We communicate via our facebook page, volunteering to host each week. Participating in HH is a good way to promote one's blog and get to know other blogs. Some of my most read posts have been the ones that are Havel Havelim and the Kosher Cooking Carnival. A look at the list on "Top 10" on my sidebar will show you that.

4 comments:

391 is 17 * 23. to find out if a number is prime (or to factor a number), divide by prime numbers up to the square root of the number to see if any of them go in evenly. so:

391 isn't divisible by 2. (we can see that easily because it's not even - i.e. doesn't end in 2, 4 6, 8, or 0)

it's not divisible by 3 (we can see that easily because the sum of its digits is not divisible by 3)

it's not divisible by 5 (we can see that it doesn't end in 5 or 0)

it's not divisible by 7, 11 or 13 (try it and see)

I am skipping all the composite numbers along the way, because obviously if it's not divisible by 2 or 3 then it won't be divisible by 4 or 6 either.

so now we are up to 17 - bingo! and we get the other factor too: 23. 17 and 23 are both prime, so no need for any further factoring. (e.g. if we would say that 24 is divisible by 6 and 4, we can break down each of those into additional prime factors and get 3, 2, 2, 2 as the factors of 24.)